Ejector mechanism for molded articles

ABSTRACT

On the opening stroke of a movable platen of an injectionmolding machine, a rod rearwardly projecting from that platen strikes a stop and displaces an articulated linkage, hinged to the platen, which transmits the relative motion of rod and platen at a reduced rate to a set of ejector pins supported on that linkage.

United States Patent [191 Rees [ EJECTOR MECHANISM FOR MOLDED ARTICLES[75] Inventor: Herbert Rees, Toronto, Ontario,

Canada [73] Assignee: Husky Manufacturing & Tool Works Limited, Bolton,Canada [22] Filed: Feb. 16, 1971 [21] Appl. No.: 115,207

[52] US. Cl. ..425/247, 425/444, 249/68 [51] Int. Cl ..B29f l/l4 [58]Field of Search ..249/63, 66, 67, 68;

18/30 CT, 2 RC, 2 RP; 425/247, 444

[56] References Cited UNITED STATES PATENTS 2,395,100 2/1946 Caron 18/30LT 2,792,592 5/1957 McGee ..18/30 LT X 2,837,765 6/1958 Havey ....18/2RP X 3,161,918 12/1964 Zearbaugh ..18/2RPX 3,418,684 12/1968 Collins..18/2 RP 3,614,810 10/1971 Schmier... .....249/68 X 2,71 1,567 6/1955Knapp ..249/68 3,448,488 6/ 1969 Kiraly ..249/68 X 2,946,102 7/1960Mills .l8/2 RP X 3,362,046 1/1968 Blumer ..18/2 RP X 3,498,581 3/1970Judson ..249/67 FOREIGN PATENTS OR APPLICATIONS 201,286 12/ 1958 Austria..249/68 Primary Examiner-J. Howard Flint, Jr. Attorney-Karl F. Ross [57] ABSTRACT On the opening stroke of a movable platen of aninjection-molding machine, a rod rearwardly projecting from that platenstrikes a stop and displaces an articulated linkage, hinged to theplaten, which transmits the relative motion of rod and platen at areduced rate to a set of ejector pins supported on that linkage.

8 Claims, 3 Drawing Figures PATENTED 1 1973 SHEET 1 [1F 2 FIG.|

FIG.2

INVENTOR,

HERBERT REES BY gm 9- ATTORNEY PATENHiH 3,726,625

sum 2 OF 2 FIG.3

INVENTOR,

HERBERT REES BY w iKm" ATTORNEY EJECTOR MECHANISM FOR MOLDED ARTICLES Mypresent invention relates to a mechanism for operating one or moreejector pins or equivalent thrust members to dislodge molded articlesfrom their seats in a movable portion of a split mold.

In conventional injection-molding machines, a platen carrying themovable mold portion is reciprocable (generally on a set of tie rods)between a forward or closed-mold and a retracted or open-mold position,this reciprocation occurring in timed relationship with the movement ofan injection piston introducing the hardenable plastic mass into thecavity or cavities of the closed mold. Each cavity is provided with anejector, such as a pin slidable in the direction of reciprocation, whichprojects rearwardly from the movable platen and strikes an abutment asthe platen retreats, thereby advancing with reference to the platenagainst the force of a biasing spring to enter the mold cavity and toeject the article seated therein.

With high-speed molding machines the impact between the ejector and afixed stop on the machine bed tends to become objectionably violent andentails the danger of damage to the molded parts.

Thus, the object of my present invention is to provide means forsoftening this impact without sacrificing the positive action ofconventional ejection mechanisms and with preservation of theiradjustability to accommodate different molds and stroke lengths.

This object is realized, in accordance with my present invention, by theprovision of an articulated linkage on the movable platen, the elementsof this linkage forming a pair of positively interconnected junctionswhich move at different rates relative to the platen whereby a pushermember coupled with the faster-moving junction, upon engaging a fixedstop on' the machine bed, causes a thrust member coupled to theslower-moving junction to advance at reduced speed with consequentlessened impact upon the molded article to be discharged.

In a preferred embodiment, the articulated linkage is of the knee-actiontype and comprises a pair of symmetrically disposed toggle joints eachhaving an engaged end pivoted to the movable platen and a free endfulcrumed on a cross-link which may be a bar, a frame or a plate andwhich carries at least one ejector pin for each mold cavity. By virtueof the symmetrical arrangement of the two toggle joints, this cross-linkstays parallel to the movable platen throughout its displacementrelative thereto so that the ejector pin or pins may be rigidlyconnected therewith.

According to another advantageous feature of my invention, the end ofthe pusher member proximal to the platen is connected with the kneepoints of the two symmetrical toggle joints via a further toggle joint,the linkage thus constituted converting a linear motion of the pusherrelative to the platen into a harmonic motion progressively acceleratingfrom standstill and approaching the speed of the pusher within a givenoperating range.

The above and other features of my invention will be described in detailhereinafter with reference to the accompanying drawing in which:

FIG. 1 is a side-elevational view, partly in section, of

a portion of an otherwise conventional injection-molding machineincorporating an ejection machanism according to the invention;

FIG. 2 is a top plan view of the mechanism shown in FIG. 1; and

FIG. 3 is a side-elevational view of the same mechanism in an alternateposition.

In FIG. 1 I have shown at 10 the bed of an injectionmolding machinecomprising a fixed platen 11 and a movable platen 12 supportingrespective mold portions 13 and 14. A portion 15 of the machine frame,rigid with bed 10, carries a set of tie rods 16 whose forward ends areanchored to stationary platen 11 and on which the movable platen 12 ishorizontally slidable. At 17 I have shown part of an injection cylinderby which hot plastic material is periodically introduced through a spruegate 18 into several cavities 19 of mold 13, 14, the molded articlesremaining seated in the cavityforming recesses of the mold portion 14when the mold is opened by a leftward retraction of platen 12.

Each cavity 19 is served by an ejector pin 20 whose front end iswithdrawn from the cavity when the mold is closed, as in FIG. 1 and 2,and whose rear end is fixedly secured to a supporting plate 21 parallelto platen 12. A

rearward extension of this platen, in the form of a guide sleeve 22supported by legs 23, is traversed by a pusher rod 24 terminating in ahead 25 which confronts the frame 15. A spring 26, inserted betweensleeve 22 and head 25, urges the rod 24 toward the rear, i.e. in thedirection of an adjustable stop 35 on frame 15; pins 20 have collars 27which, by coming to rest against the ends of respective sockets 28 inplaten l2, limit the rearward displacement of rod 24 relative to theplaten. Plate 21 is connected with platen 12 by an articulated linkagewhich comprises two symmetrical toggle these arms are so chosen that, asshown in FIG. 1, all

three toggle joints are almost or exactly in their fully extendedpositions so that any forward displacement (to the right) of rod 24relative to platen 12 results in a very slow initial advance of theplate 21 toward the platen; thus, the combined length of arms 32' and32" approximately equals the spacing of the outer ends of arms 29', 29"or 30', 30". The rate of relative plate motion accelerates as the jointsbuckle through until, at the end of the range of displacement and asillustrated in FIG. 3, the tips of pins 20 fully penetrate the recessesof mold portion 14 to eject the molded articles therefrom.

The reciprocation of platen 12 is accomplished by a pair of rams 34which are connected within frame 15 with a conventional drive mechanismsynchronized with the piston drive of injection cylinder 17. As theplaten 12 is retracted to open the mold, head 25 of rod 24 strikes theabutment 35 to actuate the articulated linkage 29'-32', 29"32" withresulting relative displacement of pins 20 at a fraction of the absoluteplaten velocity.

The adjustability of abutment 35 (and possibly of other parts of theejector mechanism such as the collars 27 on pins 20) enables the startand the extent of the ejection stroke to be adapted to the shape of themold cavities. In some instances, the head 25 could be in continuouscontact with the stop 35 or some other part of the frame so that thetoggle joints will start buckling upon inception of the mold-openingstroke, the differential motion of the pins and the mold portion 14insuring that the articles to be ejected have sufficient clearance frommold portion 13 before being dislodged from their seats.

It will be evident that the articulated linkage located in a verticalmidplane of the movable platen 12, according to the illustratedembodiment, could also be disposed in a horizontal plane and that, ifdesired, several such linkages in parallel or intersecting planes couldbe used simultaneously. In a machine with a central ram for thereciprocating of platen 12, for example, ejector pins on opposite sidesof the ram axis could be operated by separate harmonic drives each ofthe type herein disclosed.

I claim:

1. In a molding machine comprising a split mold including a movableplaten reciprocable on a bed between an open-mold and a closed-moldposition, piston means for reciprocating said movable platen, injectionmeans for introducing a hardenable mass into the closed mold to form atleast one article therein, said movable platen being provided with aseat for said article, and ejector means effective upon the opening ofsaid mold to dislodge said article from said seat, the improvementwherein said ejector means comprises an articulated linkage on saidplaten independent of said piston means and provided with a pair ofpositively interconnected junctions movable at different rates relativeto said platen, pusher means coupled with the faster-moving junction,stop means on said bed spaced from said pusher means in said open-moldposition but engageable with said pusher means for advancing same withreference to said platen upon movement of the latter toward saidopen-mold position, and thrust means on said linkage extending from theslower-moving junction toward said seat.

2. The improvement defined in claim 1, further comprising spring meansbiasing said pusher means in the direction of said stop means.

3. The improvement defined in claim I wherein said linkage includes apair of symmetrical toggle joints with engaged ends pivoted to saidplaten and with free ends interconnected by a cross-link generallyparallel to said platen, said thrust means being secured to saidcrosslink, said toggle joints having knee points connected to saidpusher means.

4. The improvement defined in claim 3 wherein said pusher meanscomprises an elongate member having a rear extremity confronting saidstop means and having a front extremity connected with said knee points.

5. The improvement defined in claim 4 wherein said movable platen isprovided with a rearward extension slidably supporting said elongatemember.

6. The improvement defined in claim 4 wherein said linkage includes afurther toggle joint connecting said front extremity with said kneepoints.

7. The improvement defined in claim 6 wherein the spacing of saidengaged ends on said platen substantially equals the spacing of saidfree ends on said crossg: The improvement defined in claim 7 whereinsaid further toggle joint comprises a pair of arms with a combinedlength substantially equaling said spacing.

1. In a molding machine comprising a split mold including a movableplaten reciprocable on a bed between an open-mold and a closed-moldposition, piston means for reciprocating said movable platen, injectionmeans for introducing a hardenable mass into the closed mold to form atleast one article therein, said movable platen being provided with aseat for said article, and ejector means effective upon the opening ofsaid mold to dislodge said article from said seat, the improvementwherein said ejector means comprises an articulated linkage on saidplaten independent of said piston means and provided with a pair ofpositively interconnected junctions movable at different rates relativeto said platen, pusher means coupled with the faster-moving junction,stop means on said bed spaced from said pusher means in said open-moldposition but engageable with said pusher means for advancing same withreference to said platen upon movement of the latter toward saidopen-mold position, and thrust means on said linkage extending from theslower-moving junction toward said seat.
 2. The improvement defined inclaim 1, further comprising spring means biasing said pusher means inthe direction of said stop means.
 3. The improvement defined in claim 1wherein said linkage includes a pair of symmetrical toggle joints withengaged ends pivoted to said platen and with free ends interconnected bya cross-link generally parallel to said platen, said thrust means beingsecured to said cross-link, said toggle joints having knee pointsconnected to said pusher means.
 4. The improvement defined in claim 3wherein said pusher means comprises an elongate member having a rearextremity confronting said stop means and having a front extremityconnected with said knee points.
 5. The improvement defined in claim 4wherein said movable platen is provided with a rearward extensionslidably supporting said elongate member.
 6. The improvement defined inclaim 4 wherein said linkage includes a further toggle joint connectingsaid front extremity with said knee points.
 7. The improvement definedin claim 6 wherein the spacing of said engaged ends on said platensubstantially equals the spacing of said free ends on said cross-link.8. The improvement defined in claim 7 wherein said further toggle jointcomprises a pair of arms with a combined length substantially equalingsaid spacing.